1. Field of the Invention
This invention relates to an ultrasound diagnostic apparatus designed to detect the velocity of an organ or a tissue in a body.
2. Description of the Related Art
General-purpose ultrasound diagnostic apparatuses can operate in any one of different modes such as a B mode, an M mode, an FFT Doppler mode, and a color Doppler mode. In some cases, a diagnosis on arteriosclerosis is based on an ultrasound diagnosis on a carotid artery which uses a general-purpose ultrasound diagnostic apparatus. Specifically, the ultrasound diagnosis is implemented by using shape information generated by the B mode and the M mode of operation of the apparatus, and blood velocity information provided by the FFr Doppler mode or the color Doppler mode of operation of the apparatus.
When the general-purpose ultrasound diagnostic apparatus operates in the B mode, the inside diameter of a blood vessel, the thickness of a blood vessel wall, and the conditions of a morbid protuberance can be evaluated from information provided by the apparatus. When the general-purpose ultrasound diagnostic apparatus operates in the M mode, a time-domain change of a blood vessel diameter in response to a heartbeat can be evaluated from information provided by the apparatus. When the general-purpose ultrasound diagnostic apparatus operates in the FET Doppler mode or the color Doppler mode, the rate of a blood flow in a blood-vessel strangulated portion caused by a morbid protuberance can be evaluated from information provided by the apparatus.
As previously mentioned, the conditions of a morbid protuberance can be evaluated by using the B mode of operation of the general-purpose ultrasound diagnostic apparatus. Specifically, the presence and the size of the morbid protuberance are observed via the apparatus. In addition, the brightnesses in an ultrasound-echo-based image (a B mode image or a sectional image) displayed on a monitor of the apparatus are observed. The conditions of the morbid protuberance are judged from the size information and the brightness information.
Generally, a morbid protuberance caused by a thrombus is indicated as an image portion having a low brightness. Therefore, in some cases, such a morbid protuberance fails to be found by using the B mode of operation of the general-purpose ultrasound diagnostic apparatus.
As previously mentioned, the conditions of a morbid protuberance are judged from size information and brightness information during the B mode of operation of the general-purpose ultrasound diagnostic apparatus. Since the brightness information is used, it is difficult to quantitatively evaluate the conditions of the morbid protuberance.
Japanese published unexamined patent application 9-313485 discloses an ultrasound apparatus for diagnosing the conditions of a tissue in a body which uses tissue Doppler imaging. The apparatus in Japanese application 9-313485 measures motion of the tissue relative to an ultrasound probe. Accordingly, it is difficult for the apparatus to detect a self-motionless suspended portion in a moving tissue. In addition, it is difficult for the apparatus to detect motion of a tissue in a direction perpendicular to an ultrasound beam.
Japanese published unexamined patent application 10-5226 discloses an ultrasound apparatus for diagnosing the conditions of a tissue in a body. In the apparatus of Japanese application 10-5226, information is generated which represents the amplitude and the phase of an electric signal resulting from detection of ultrasound echoes. Then, the instantaneous position of an object is decided on the basis of the amplitude and phase information in a least-squares method. Accurate tracking on the object is implemented in response to the decided instantaneous position thereof. The accurate tracking makes it possible for the apparatus to correctly detect self-motion of a portion in a tissue which is being greatly moved by a heartbeat.
The apparatus of Japanese application 9-313485 and the apparatus of Japanese application 10-5226 can detect only a component of the velocity of an object in a direction along the acoustic line of an ultrasound beam.
Some ultrasound diagnostic apparatuses for measuring a blood flow rate are equipped with arrangements which implement correction related to the angle between the direction of a blood vessel and the direction of the acoustic line of an ultrasound beam. This correction method can not be applied to detection of the velocity of an organ or a tissue which is moving in various directions.